Least invasive surgical techniques have gained significant popularity because of their ability to accomplish outcomes with reduced patient pain and accelerated return of the patient to normal activities. Arthroscopic surgery, in which the intra-articular space is filled with fluid, allows orthopedic surgeons to efficiently perform procedures using special purpose instruments designed specifically for arthroscopists. Among these special purpose tools are various manual graspers and biters, powered shaver blades and burs, and electrosurgical devices. During the last several years specialized arthroscopic electrosurgical electrodes called ablators have been developed. Exemplary of these instruments are ArthroWands manufactured by Arthrocare (Sunnyvale, Calif.), VAPR electrodes manufactured by Mitek Products Division of Johnson & Johnson (Westwood, Mass.) and electrodes by Oratec Interventions, Inc. (Menlo Park, Calif.). These ablator electrodes differ from conventional arthroscopic electrosurgical electrodes in that they are designed for the bulk removal of tissue by vaporization rather than the cutting of tissue or coagulation of bleeding vessels. While standard electrodes are capable of ablation, their geometries are not efficient for accomplishing this task. While the tissue removal rates of ablator electrodes are lower than those of shaver blades, ablators are used because they achieve hemostasis (stop bleeding) during use and are able to efficiently remove tissue from bony surfaces. Ablator electrodes are used in an environment filled with electrically conductive fluid.
Ablator electrodes are produced in a variety of sizes and configurations to suit a variety of procedures. For example, ablators for use in ankle or elbow arthroscopy are smaller than those used in the knee or shoulder. In each of these sizes, a variety of configurations are produced to facilitate access to various structures within the joint being treated. These configurations differ in the working length of the electrode (the maximum distance that an electrode can be inserted into a joint), in the size and shape of their ablating surfaces, and in the angle between the ablating face and the axis of the electrode shaft. Electrodes are typically designated by the angle between a normal to the ablating surface and the axis of the electrode shaft, and by the size of their ablating surface and any associated insulator.
Primary considerations of surgeons when choosing a particular configuration of ablator for a specific procedure are its convenience of use (i.e., its ease of access to certain structures) and the speed with which the ablator will be able to complete the required tasks. When choosing between two configurations capable of accomplishing a task, surgeons will generally choose the ablator with the larger ablating surface to remove tissue more quickly. This is particularly true for procedures during which large volumes of tissue must be removed. One such procedure is acromioplasty or the reshaping of the acromion. The underside of the acromion is covered with highly vascular tissue which may bleed profusely when removed by a conventional powered cutting instrument such as an arthroscopic shaver blade. Ablator electrodes are used extensively during this procedure since they are able to remove tissue without the bleeding. Ablation in the area under the acromion is most efficiently accomplished using an electrode on which a line normal to the ablating surface is perpendicular to the axis of the ablator shaft. Such an electrode is designated as a “90 Degree Ablator” or a “side effect” ablator. Exemplary of such electrodes are the “3.2 mm 90 Degree Three-Rib UltrAblator” by Linvatec Corporation (Largo, Fla.), the “90 Degree Ablator” and “90 Degree High Profile Ablator” by Oratec Interventions, the “Side Effect VAPR Electrode” by Mitek Products Division of Johnson and Johnson, and the “3.5 mm 90 Degree Arthrowand,” “3.6 mm 90 Degree Lo Pro Arthrowand,” and “4.5 mm 90 Degree Eliminator Arthrowand” by Arthrocare Corporation.
The above-mentioned 90 degree ablator electrodes may be divided into two categories: (i) electrodes of simple construction, wherein RF energy is conducted to the ablator tip by an insulated metallic rod or tube; and (ii) electrodes of complex construction, which use wires to conduct power to the tip.
Ablator electrodes having a simple geometry are produced by Linvatec Corporation (as described in U.S. Pat. No. 6,149,646) and Oratec Interventions, Inc. and are monopolar instruments, that is, the circuit to the electrosurgical generator is completed by a dispersive pad (also called a return pad) placed on the patient at a distance from the surgical site. A suitable geometry, either ribbed or annular, is formed on the distal end of the ablator rod, and the distal tip of the rod is bent to a predetermined angle to the axis of the rod. For a 90 degree electrode, this predetermined angle is 90 degrees. The rod diameter may be locally reduced in the region near its distal tip to reduce the radius of the bend. The rod is insulated up to the ablation face on the rod distal tip using polymeric insulation. A ceramic insulator may be added to prevent charring of the polymeric insulation.
Ninety degree ablator electrodes having a complex construction, such as those in which the active electrode is attached to the electrosurgical generator via cables passing through an elongated tubular member, are produced by Arthrocare Corporation (U.S. Pat. No. 5,944,646 and others) and the Mitek Products Division of Johnson & Johnson. Typically, these electrodes are bipolar instruments, having a return electrode on the instrument in close proximity to the active electrode. Bipolar arthroscopy electrodes of this type are constructed of a tubular member upon which one or more electrodes (herein referred to as active electrodes) are mounted and connected via one or more cables to an electrosurgical generator, the leads passing through the lumen of the tubular member. The active electrodes are isolated electrically from the tubular member and rigidly mounted to the tubular member by a ceramic insulator affixed to the tubular member. The tubular member is electrically isolated from the conductive fluid medium by a polymeric coating, except for an area at the distal tip in the vicinity of the active electrode. The proximal end of the tubular member is connected electrically to the electrosurgical generator via one or more cables. During use, current flows from the active electrode through the conductive fluid medium to the uninsulated portion of the tubular member, which functions as a return electrode in close proximity to the active electrode.
While the construction of these complex bipolar electrodes is more expensive than that of the other monopolar electrodes, this construction allows the design of 90 degree ablators with large ablating surfaces, the surfaces being only slightly elevated above the outer surface of the tubular member. This “low profile” design is desirable in that it allows surgeons to pass the electrode through smaller diameter cannulae than would be possible with electrodes of other designs.
Electrodes of simple design and having a single-piece rod with far distal bend for an active electrode have certain design limitations with regard to the positioning of the ablating surfaces. Low profile, 90 degree designs require that the bend radius be extremely tight and placed in extremely close proximity to the ablating surfaces. Such a bend may be accomplished by reducing the cross-sectional area of the rod in the area to be bent. Alternatively, extra length may be added to the distal tip of the rod, the rod bent and the extra material removed prior to forming of the ablation surfaces.
Each of these approaches has limitations. First, in the case of reduced cross-sectional area, the active electrode of an ablator device becomes very hot during use because of interaction of the ablative arc with the metal of the electrode. During use, a portion of the electrode is lost due to vaporization of the material. Melting of the polymeric insulation on the ablator rod may occur if the temperature of the metal rod becomes excessively high. This melting may be minimized in the region adjacent to the ablating surface through use of a ceramic insulator between the active electrode and the polymeric insulation. Cooling of this region also occurs through conduction of heat away from the region proximally through the electrode rod. The degree of cooling depends on the cross-sectional area of the electrode rod. By reducing the cross-sectional area of the rod to achieve a far distal bend, the temperature of the electrode in the region adjacent to the ablating surface is increased and melting of the polymeric insulation may occur.
Second, when extra material is added to the rod to permit bending and then machined away so as to allow forming of the ablating surfaces, any but the simplest active electrode geometry will require complex machining operations. For instance, to produce a ribbed geometry with a ceramic insulator, such as that of the Linvatec 3-Rib ablator, the extra material must first be removed, a precise cylindrical surface perpendicular to the axis of the rod formed to allow installation of the ceramic insulator and, finally, the ribs formed by grinding or wire EDM. Each of these operations requires that the rod be precisely and repeatably located, a difficult task on an item such as a bent rod.
As mentioned previously, interaction of the ablative arcs with the active electrode causes material loss through vaporization and combustion of the metallic material. Combustion of the electrode material will affect the characteristics of the plasma of which the arc is composed. In some cases, it is desirable to use a combustible electrode material such as titanium to achieve certain desired ablation process characteristics. For instance, it is thought that the extreme brightness of the arc causes some photoablation of tissue. This photoablation may be maximized by increasing the brightness of the arc. In turn, this increase in brightness may be achieved by using a combustable electrode material such as titanium. Ablators of complex construction are able to easily use a variety of active electrode materials because the electrodes are a small part of a larger complex assembly. On electrodes of simple construction, the selection of the active electrode material is not as simple since the entire electrode rod is made from the same material as the active electrode tip. Use of a material like titanium can add significantly to the material cost and the machining cost of the product.
A recent addition to ablator electrodes is a means of aspiration to remove bubbles from the surgical site. During arthroscopic electrosurgery, tissue is vaporized producing steam bubbles which may obscure the view of the surgeon or displace saline from the area of the intra-articular space which the surgeon wishes to affect. During ablation, the amount of bubbles produced is even greater than the amount produced when using other electrodes, since fluid is continually boiling at the active electrode during use. Ideally, flow through the joint carries these bubbles away. Nevertheless, in certain procedures, this flow is frequently insufficient to remove all of the bubbles. The aspiration means on an aspirating ablator removes some bubbles as they are formed by the ablation process, and others after they have collected in pockets within the joint. The ablator aspiration means is connected to an external vacuum source which provides suction for bubble evacuation.
There are two types of aspiration on currently available ablator products, which may be divided into two categories according to their level of flow.
High-flow ablators have an aspiration tube having an diameter larger than the elongated distal portion of the probe and coaxial with the axis of the ablator elongated portion so as to form a passage between the elongated portion and the aspiration tube. Bubbles and fluid are drawn into the passage through the distal opening and/or openings formed in the tube wall near its distal tip. High-flow ablators may decrease the average joint fluid temperature by removing heated saline (waste heat since it is an undesirable byproduct of the process) from the general area in which ablation occurs. The effectiveness of the aspiration, both for removal of bubbles and for removal of waste heat, will be affected by the distance between the opening through which aspiration is accomplished and the active electrode. The distal tip of the aspiration tube is generally several millimeters distant proximally from the active electrode, so as to not to obstruct the surgeon's view of the electrode during use. Decreasing this distance is desirable since doing so will increase the effectiveness of the aspiration, however, this must be accomplished without limiting the surgeon's view or decreasing the ablators ability to access certain structures during use.
Low-flow ablators aspirate bubbles and fluid through gaps in the ablating surfaces of the active electrode and convey them from the surgical site via a tube passing through the ablator tubular member, or via a cannulation in the ablator rod. A low-flow ablator will require increased power to operate as effectively as a high-flow aspirating ablator because the low-flow aspiration is drawing hot saline from the active site of a thermal process. In the case of low-flow ablators, the heat removed is necessary process heat rather than the waste heat removed by high-flow ablators. As a result, low-flow aspirating ablators generally require higher power levels to operate than other ablators, thereby generating more waste heat and increasing undesirable heating of the fluid within the joint.
Each of the above-described aspirating ablators has its drawbacks. In high-flow aspirating ablators, the aspiration tube increases the diameter of the device and requires the use of larger cannulae. In low-flow aspirating ablators, the devices frequently clog with charred tissue.
Accordingly, it is an object of this invention to produce a low-cost monopolar electrosurgical ablator electrode of simple construction, having RF energy conducted to the active electrode through the material of the elongated member, and having a large ablating surface and a low profile with the ablation surface displaced only a small distance above the periphery of the outer surface of the elongated body.
It is also an object of this invention to produce a monopolar electrosurgical ablator of simple construction and comprising an active electrode which may be of a material different from the material forming the elongated body of the electrode.
It is also an object of this invention to produce a monopolar electrosurgical ablator electrode having a high-flow aspiration means, which does not increase the diameter of the electrode elongated portion and which is provided with multiple openings in the ablator distal tip area, at least one of which is in close proximity to the active electrode.